1. Field of the Invention
The present invention relates to a data processing device for a laser printer, a digital copying machine, a facsimile device, etc., in particular, a data processing device including an apparatus for simultaneously or almost simultaneously reading out plural lines of image, and a method therefor.
2. Discussion of the Background
Conventionally, regarding the image forming apparatus for use in the laser printer, a digital copying machine, a facsimile device, etc., there has been used a single beam type image forming apparatus carrying therein a writing-in apparatus in which the scanning operation is performed on the photosensitive body in the main scanning direction with a line of laser beam emitted from a recording light source composed of a laser diode modulated by the image data by use of a scanning medium constructed with a polygon mirror, and the image of one line is written in respectively per one line in order on the photosensitive body by moving the photosensitive body in the subscanning direction.
Furthermore, there has been proposed a multiple beam type image forming apparatus carrying therein a writing-in apparatus in which the scanning operation is performed in the main scanning direction on the photosensitive body with the plural lines of the laser beam emitted from the recording light source composed of plural laser diodes independently modulated by the image data, and the image of plural lines is written in on the photosensitive body simultaneously or almost simultaneously by moving the photosensitive body in the subscanning direction.
Since such multiple beam type image forming apparatus can perform the operation of writing in the image of plural lines simultaneously or almost simultaneously by use of one surface of the polygon mirror, the apparatus is featured in that the image can be written in with high speed by use of a low-revolution polygon mirror and a low-output-power laser diode.
In the case of inputting the image data into the above-mentioned image forming apparatus, the single beam type image forming apparatus carrying therein a writing-in apparatus including a single laser diode or the multiple beam type image forming apparatus carrying therein another writing-in apparatus including plural laser diodes is employed. However, regardless of the type of such image forming apparatus to be employed, the image data per one line are inputted pixel by pixel, or pixels by pixels by incrementing the address in the main scanning direction with a predetermined input clock after resetting the address in the main scanning direction with a line synchronization signal, and then such operations are repeated.
In the multiple beam type image forming apparatus, since the image data of plural lines are written in simultaneously or almost simultaneously by use of the plural lines of the laser beam from the plural laser diodes, it is necessary to distribute simultaneously or almost simultaneously the image data to be inputted line by line to the image data of the plural lines synchronized with the print clock for modulating the plural laser diodes.
If the scanning position of the plural lines of laser beam from the plural laser diodes is aligned in the main scanning direction, it may be allowed that a single laser diode is modulated with the image data of one line taking a timing with one laser beam, and the remaining respective diodes are respectively modulated with the image data per one line taking the same timing as mentioned above.
However, it may be optically difficult to align the plural laser beam in the main scanning and to keep the pitch of the plural laser beams in the subscanning direction to a value, for instance, 63.5 .mu.m (400 dpi). Furthermore, since it is required to accomplish a function of enabling to change the density of the writing-in, it may turn out to be further very difficult to change over the pitch of the plural laser beams in the subscanning direction in accordance with the density of the writing-in.
In such situation, the scanning positions of the plural lines of the laser beams are parted from each other to some extent, and the laser light emitting section including the plural laser diodes is rotated. Thereby, methods of adjusting the pitch of the plural lines of the laser beam in the subscanning direction and changing over the pitch thereof have been proposed hitherto. In such system, since the phases in the light emission timings of the plural lines of the laser beam are different from each other, it is necessary to individually control the light emission timings.
The published specification of Japanese Published Patent Publication No. 8-34537/1996 describes the construction and the system of a buffer memory regarding the multiple beam type image forming apparatus. It further describes that the image data are read out from the buffer memory by use of an address signal generated by plural counting media for counting plural clock signals generated on the basis of plural beam detecting signals and a common standard clock, and plural light beams are modulated with the image data thus read out.
Regarding the multiple beam type image forming apparatus described in the published specification of Japanese Patent Publication No. 8-34537/1996, to state more concretely, such image forming apparatus in which a photosensitive member is scanned with n light beams (n is integer equal to or more than 2) and the synchronization is taken in the main scanning direction on the basis of a detection signal for detecting n beams obtained by detecting the aforementioned n light beams by use of a beam detecting media is featured by a synchronization clock generating medium for generating n clock signals individually synchronized with the n beam detecting signals, and n counting media for respectively counting one of the aforementioned n clock signals in order to generate n address signals to be renewed individually in synchronism with the aforementioned n beam detecting signals. Furthermore, the image forming apparatus is featured in that, the respective memorizing media, in parallel operation with the writing-in of the image data to one buffer memory, the image data are read out from the other buffer memory by use of one of the n address signals to be renewed individually in synchronism with the aforementioned n beam detecting signal.
Consequently, the n image data of the output timing in accordance with the detecting timing of the n light beams can be outputted as the signal for modulating the aforementioned n light beams.
On the other hand, there has existed a so-called "smoothing process" for deciding the lighting-up time and the lighting-up timing for the laser beam of the pixel to be noted in accordance with the information of the noted pixel and the circumferential pixel thereof, and for reducing the extents of the slanted line of the image edge portion and the notches of the circular arc thereof.
In such smoothing process, etc., that is, an image forming process requiring the information of the circumferential pixels of the noted pixel, plural lines of the line memory are prepared, and then the feature of the noted pixel is extracted and thereby the image data are decided in accordance with the information of the noted pixel and the circumferential pixels thereof by use of the matrix formed reading out at the same time the plural lines of the image data stored in the line memory.
The aforementioned published specification of Japanese Published Patent Publication No. 8-34537 describes that, in the multiple beam type image forming apparatus, the timing of scanning the plural lines of the light beam are arranged properly (made uniform). However, the above specification does not describe that the image data to be inputted line by line are distributed to the plural lines of the image data employed in order to respectively modulate the plural lines of the plural light beams. Furthermore, since the image data read out from the plural buffer memories are respectively asynchronous, not only the above n counting media but the signal process circuits for processing the read-out image data are required corresponding to the predetermined numbers of the light beams, and consequently, the structure of the image forming apparatus becomes further complicated. As the result, the manufacturing cost may be increased inevitably.
Furthermore, the conventional image forming process such as smoothing process has utilized an original line memory (of its own). On the other hand, the other operations of converting the speed of the image data and transforming the image data to the multiple beam have been performed by the other memory.